if ("a" in window) {
var a = 1;
console.log(a)
}
console.log(a);
function a() {
console.log(this);
}
a.call(null);
I don"t understand why this error was reported. Ask for advice
if ("a" in window) {
var a = 1;
console.log(a)
}
console.log(a);
function a() {
console.log(this);
}
a.call(null);
I don"t understand why this error was reported. Ask for advice
js the function declaration is promoted to the top during execution, so when you execute the if statement, a is replaced with a numeric type variable with a value of 1 , not a function type. You can read the following articles about variable promotion, such as https://juejin.im/post/59905b...
//
function a() {
console.log(this);
var a;
if ("a" in window) {
a = 1;
console.log(a)
}
console.log(a);//a1
a.call(null);
[https://segmentfault.com/a/1190000017805834][1]
your a.call () an is the basic type a = 1, not object, so it will report an error. Variable promotion is involved here. In js, the function is a first-class citizen, and the above code parses to:
function a() {
console.log(this);
}
var a;
if ("a" in window) {
a = 1;
console.log(a)
}
console.log(a);
a.call(null); Previous: What if flutter builds a development environment and VS Code is an exclamation point?
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